Passive anti-jamming antenna system

ABSTRACT

System and method for improving the interference resistance of an radio frequency (RF) antenna system through passive prescreening of the RF energy incident upon the antenna. The invention physically partitions the RF environment into two or more sectors with respect to the direction of arrival of incident energy. The power level of the RF frequencies of interest incident upon each sector is determined such that whenever the power level exceeds a given threshold, the received signal from energy incident on that sector is modified.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/234,098,filed Sep. 5, 2002 now U.S. Pat, No. 6,992,643, which is a continuationof application Ser. No. 09/774,085, filed Jan. 31, 2001, now U.S. Pat.No. 6,469,667. Each and every document, including patents andpublications, cited herein is incorporated herein by reference in itsentirety as though recited in full.

This application is related to and claims the benefit of U.S.Provisional Application No. 60/179,564 entitled “Passive Anti-JammingAntenna System.” filed 1 Feb. 2000, hereby incorporated herein in itsentirety.

FIELD OF THE INVENTION

The present invention relates to the field of antenna systems, and moreparticularly, to passive interference-suppressing antenna systems, andthe methods used therein.

BACKGROUND OF THE INVENTION

Radio Frequency (RF) jamming, i.e. intentional RF interference, occurswhen RF power is transmitted so as to interfere with the reception andinterpretation of an RF receiving system. Jamming signals may interferewith the operation of receivers such as navigation, communication, andglobal positioning system (GPS) receivers. In this sense electromagneticinterference generally, and jamming in particular, are consideredcountermeasures to the intended utilization of RF receiver systems.

A number of techniques have been developed to mitigate the deleteriouseffects of interference on RF receiver systems, including employment ofadaptive antenna systems. Adaptive antenna systems typically measure thereceived power and/or the signal or carrier to noise ratio. Thesemeasurements are utilized to modify the reception pattern of thereceiving antenna in order to steer a null, i.e., a minimal receptionregion, in the direction of a interference source and/or steer a gainmaximum in the direction of a desired information signal source.

One example of such an adaptive antenna system counter-countermeasure isreferred to as the Controlled Reception Pattern Antenna (CRPA). The CRPAoperates by receiving electromagnetic energy and feeding it into anantenna array controller unit. Upon detection of received interferencepower above a threshold, the antenna array controller adaptively altersthe antenna array's reception pattern to attenuate the gain in thedirection of the interference. It does this by applying amplitude andphase weights to the auxiliary elements in the array and repeatedlytaking power measurements of the incident interference. If a weight isapplied to an element and the received power of the interference (orjamming signal) improves (decreases) the antenna array controllerdecides that the applied weight was a good choice and the weight issaved. If the received interference power increased, or remained thesame, however, the antenna array controller decides that the appliedweight was not a good choice and it returns to the previous weight forthat element. The Antenna Electronics (AE) unit keeps repeating thisprocess until the received power level has returned to itspre-interference level, which implies that a null has been successfullysteered in the direction of the interference.

The GPS Antenna System (GAS) is a next generation adaptive antenna arraysystem that is the follow-on to the CRPA/AE. Beam steering in a GAS isaccomplished by maximizing the signal-to-noise, or carrier-to-noise,ratio, which indicates that a maximum in the array's reception has beensteered in the direction of the intended signal source. The GAS isbelieved to operate much faster than the CRPA/AE since it incorporatesmodern processors.

Both CRPA/AE and GAS adaptive systems have a number of drawbacks. Theyare limited to mitigating a maximum of 6 interferers and are ineffectiveagainst some types of simple jammers as well as some types of advancedjamming waveforms. Also, the nulls produced are relatively wide andthese systems require software modifications to deal with changes injamming technology

SUMMARY OF THE INVENTION

A system and method for receiving transmitted electromagnetic signals inthe presence of interference is disclosed. In one embodiment, thepresent invention improves the interference resistance of an existing RFantenna receiver system by passively prescreening the electromagneticenergy incident upon the antenna. One embodiment includes physicallypartitioning the incident electromagnetic RF environment of theprotected system into two or more fields of view, or sectors, andevaluating the power level of the RF frequencies of interest incidentupon each sector. In one embodiment, the passage of the incidentfrequencies of interest by a sector to the protected receiver system isprevented whenever the power level of any RF frequency of interestexceeds a given threshold. In this way, the present invention passivelymitigates the impact of intentional RF jamming and unintentional RFinterference. The physical shape of the antenna, the number of sectorsinto which the RF environment is portioned, the frequencies of interestand the threshold values are specifically tailored to the requirementsof the system being protected.

Consequently, embodiments of the present invention eliminate therequirement for an algorithmic determination of an interferer'spresence, its location and its subsequent elimination. In someembodiments, it operates in a single step, without the requirement forsoftware. Also, narrow nulls may be constructed and their width may bemodified by varying the geometry and the number of individual sectorspartitioning the RF environment.

BRIEF DESCRIPTION OF THE FIGURES

The various advantages of the invention will become apparent to oneskilled in the art by reading the following specification and byreference to the following drawings, which are provided by way ofexample and do not limit the broad application of the invention.

FIG. 1 depicts the RF environment partitioning aspect of the inventionfor two or more sectors.

FIG. 2 shows a block diagram of the major functional components of oneembodiment of the present invention that utilizes sector-specificantenna elements.

FIG. 3A shows a top view of an antenna having hex-sided sectors inaccordance with one embodiment of the invention.

FIG. 3B shows a sectional view of an antenna having hex-sided sectors inaccordance with one embodiment of the invention.

FIG. 4 shows a diagram of two adjacent sectors in an interferencemitigation antenna system in accordance with one embodiment of theinvention.

FIG. 5 shows the interaction of an RF wave incident upon an absorbercoated partition separating antenna sectors in accordance with oneembodiment of the invention.

FIG. 6 shows the occurrence of total internal reflection at the boundarybetween an antenna partition and its absorbent layer.

FIG. 7 shows the occurrence of total internal reflection at the boundarybetween an antenna partition absorbent layer and the interior of asector.

FIG. 8 shows a diagram of the geometry of an antenna array for analyzingantenna sectors' fields of view.

FIG. 9 shows a diagram of the rectangular placement of antenna units forminimal coverage by two antennas.

FIG. 10 shows additional details of the diagram shown in FIG. 8.

DETAILED DESCRIPTION OF THE DRAWINGS

The following description relates to a system and method for improvingthe interference resistance of an antenna system through passiveprescreening of the RF energy incident upon the antenna. Preferredembodiments of the invention physically partition the RF environmentinto two or more sectors with respect to the direction of arrival ofincident energy. In a preferred embodiment, the power level of the RFfrequencies of interest incident upon each sector is monitored such thatwhenever the power level exceeds a threshold, the received signalgenerated by energy incident upon that sector is filtered, attenuated,or blocked from reaching a downstream device, e.g., a receiver.

Referring to FIG. 1 there is shown a notional diagram of an antennasystem 10 of the present invention and the environment in which theantenna system 10 operates. A source of desired RF signals 12 transmitsa desired RF signal 14 in the direction of the antenna system 10. Thesource 12 may comprise a satellite, or other airborne or ground basedsources. One or more interference sources 16 generate interferenceenergy 18, which is incident on the antenna system 10. The interferencesources 16 may be deliberately placed by a hostile party to interferewith the reception of the desired signal, i.e. jamming, or may derivefrom other sources, either naturally occurring or man-made. Because theinterference energy 18 is often stronger than the desired signal 14, itspresence can make detection of the desired signal difficult orimpossible. An antenna system of the present invention 10 allows thedesired signal 14 to be detected in the presence of the interferenceenergy 18 by effectively isolating a portion of the interference energy.

FIG. 2 shows additional details of one embodiment of an antenna system10 of the present invention. A desired signal 14 and interference energy18 are received by a partitioning device 20. An antenna array 21includes two or more antenna elements 22, which are disposed at the baseof the partitioning device 20. The partitioning device 20 is configuredsuch that it creates spatial sectors that divide the field of view (FOV)of the antenna system 10 into two or more regions of space. The base ofeach sector is configured to define the size and shape of the top of theantenna elements 22.

Each antenna element 22 generates a received RF signal in response tothe incident energy 14 and 18 as affected by the partitioning device 20.The RF signals generated at each antenna element 22 are communicated toa processing unit 24. The processing unit 24 selectively modifiesindividual signals from individual antenna elements 22 and either blocksthe signal entirely, or communicates a modified, e.g., filtered orattenuated, signal to a combiner unit 26 and then to a receiver 28. Theprocessing unit 24 need not contain active components. Signals from theother antenna elements 22 are unmodified by the processing unit 24 andreach the combiner 26 and receiver 28 substantially unattenuated.

In a preferred embodiment of the invention, the processing unit 24measures the power of each signal coming from each antenna element 22,and hence from each corresponding sector in the partitioning device 20.If the power level from any sector exceeds a predetermined threshold,the processing unit 24 blocks the energy from that sector from reachingthe receiver 28 or attenuates that energy. This is done because signalsexceeding the threshold are likely to be from an interferer, and notfrom the desired signal source. The exact level of the threshold willdepend on the specific parameters of the particular antenna system. Forexample, the threshold should be above the maximum expected signalstrength of the desired signal to avoid blocking the desired signal. Theprocessing unit 24 monitors the incoming RF signals from each segment,so that changes in the location and strength of the interference will bereadily detected and blocked or attenuated.

FIGS. 3A and 3B show two views of a partitioning device 30 in accordancewith a preferred embodiment of the invention. Each sector 32 in thepartitioning device 30 has hex shaped walls. Other shapes could be useddepending on the requirement of the particular application. FIG. 3Bshows that the partitioning device 30 is hemispherical shaped incross-section. This cross-sectional shape could instead be oval or flatdepending on the application.

FIG. 4 shows an expanded cross-sectional view of two adjacent sectors 34and 36 which form part of a partitioning device such as the one shown inFIGS. 3A and 3B, in accordance with another embodiment of the invention.The sector walls 38 define the shape of each sector 34 and 36. Antennaelements 40 and 42 are disposed to the base of the sectors 34 and 36respectively.

A desired RF signal 44 is shown entering sector 36. This sector happensto be positioned such that the desired signal 44 enters the sector 36and passes unimpeded to the antenna element 42 at its base i.e., thedesired signal 44 is “on-axis” to sector 36. Since the desired signal 44will typically be below threshold, the RF energy incident on the antenna42, comprising the desired signal, will not be blocked by the processingunit 24 and will reach the receiver 28.

Interference energy 46, will generally be coming from a differentdirection than the desired signal 44, i.e., an antenna array may bedirected such that much interference energy arrives “off-axis” to atleast some sectors. There are two primary concerns with suchinterference energy. First, it is desired that the off-axis interferenceenergy 46 entering sector 36 be absorbed by the sector walls 38 and notreach the antenna element 42 to any significant degree. This will ensurethat antenna element 42 will receive only significant levels of thedesired signal and little or none of the interference energy. A secondconcern is to insure that a interference energy 46 in a sector 34adjacent to a sector receiving the desired signal, does not cross thesector wall 38 and reach that sector. Both of these situations arereferred to herein as multipath reception.

FIGS. 4-7 show embodiments of the present invention that suppressmultipath reception by the use of absorber layers 48, 50. It will beappreciated that other techniques for suppressing multipath receptionmay be employed while using the teachings of the invention. In general,the absorber layers absorb off-axis signals 46. As a result, the fullstrength of these signals 46 does not reach the antenna element 42receiving a desired signal 44, nor do the signals 46 cross over from anadjacent sector 34 to the sector 36 receiving the desired signal 44.Note that, absent filters of some sort, interfering energy that ison-axis to a sector will be received directly by the antenna element inthat sector, its strength will typically be above-threshold, thus thereceived signal from any element in that sector will be blocked orattenuated by the processing unit 24.

Referring again to FIG. 4, there is shown an off-axis signal 46 thatenters the sector 34 adjacent to the sector 36 receiving the desiredsignal 44. The volume inside sector 34 is filled with a material havingan index of refraction designated n(s,2). Likewise, the volume insidesector 36 is filled with a material having an index of refraction ofn(s,1). The sector wall 38 is preferably a dielectric (non-conducting)material that has an index of refraction of n(p). These materials may beselected based on the requirements of the particular application.

The sector wall 38 separating sectors 34 and 36 is coated on each sidewith an absorber layer 48, 50. The absorber layers 48 50 together withthe sector wall 38 minimize reflections from spatial regions outside thefield-of-view of each individual sector. In particular, the sector wall38 is coated on the sector 36 side with a first absorber layer 48,having index of refraction n(A,1). The sector wall is coated on thesector 34 side with a second absorber layer 50, having an index ofrefraction of n(A,2).

FIG. 5 shows an enlarged section of the sector wall 38 within thecircled area of FIG. 4. The off-axis signal 46 is shown travelingthrough the volume of sector 34. When signal 46 encounters the absorberlayer 50, a reflected wave 52 and a refracted wave 54 are generated. Inthis example, n(s,i)<n(A,i)<n(p), where i=1 or 2. The strengths of thereflected and transmitted components depend upon the angle of incidenceupon the boundary of absorber layer 50, the polarization state of theincident wave, and the relationship between n(s,i) and n(A,i).

The wave 54 transmitted into the absorber 50 propagates until itencounters the boundary between the absorber layer 50 and the partitionwall 38. As before, a fraction 100 of this wave is reflected back intothe absorber layer 50 and the remainder 130 is transmitted into thepartition wall 38. Again, the strengths of these reflected andtransmitted components depend upon the angle of incidence upon theboundary, the polarization state of the incident wave, and therelationship between n(A,i) and n(p). As can be seen in FIG. 5,reflected 52, 100, 110, 200, 210, 300, 310 and transmitted 54, 120, 130,220, 230, 320, 330 wave components are produced each time that apropagation wave encounters a boundary with a different material(different refractive indexes). Consequently, the absorption of off-axissignals can be controlled by the selection of the materials of thepartition wall 38, absorber layers 48 and 50, and the material withinthe sector volume.

Further control of the transmission of off-axis signals can be achievedby the use of the phenomenon known as total internal reflection (TIR).FIG. 6 illustrates the use of TIR at the boundary between the sectorwall 38 and the absorber layer 48, where, as in FIG. 5,n(s,i)<n(A,i)<n(p) and i=1 or 2. It will be appreciated that when a waveis incident upon a less dense medium (having smaller refractive index),from a more dense medium (having a larger refractive index), thereflectivity is equal to one when the angle of incidence equals an anglecalled the “critical angle”. That is, when the angle of incidence equalsthe critical angle the transmission angle reaches 90 degrees and thetransmitted wave propagates parallel to the boundary between the twomaterials. This is shown by the dotted line 56 in FIG. 6. When the angleof incidence exceeds the critical angle, the angle of transmissionbecomes imaginary and the energy is reflected back into the densermedium, as shown by lines 58, 60, etc. Note that since n(p) is greaterthan both n(A,1) and n(A,2), the wave 58-62 undergoes TIR at both theboundaries of the partition wall 38 material with the two absorber layermaterials.

FIG. 7 also illustrates the use of TIR to control the transmission ofthe off-axis signal 46. In this case, the angle of incidence of thesignal 46 and the indices of refraction of the materials is such thatwave 130 does not undergo TIR when it encounters the boundary betweenthe partition wall 38 and the absorber layer 48. However, the angle ofincidence of wave 64 at the boundary between the absorber layer 48 andthe sector volume 36 is great enough to produce TIR. Wave 68 isgenerated when the angle of incidence of wave 64 is equal to thecritical angle. When incoming waves are at less than the critical angle,there will be some component transmitted into the sector 36. However,the physical dimensions of the partitioning device 20 can be designedsuch that waves this far off-axis will effectively be prevented fromdirectly entering the sector 34 so that wave 46 will not be transmittedinto sector 36.

There are many possible permutations of refractive index relationshipsother than the conditions depicted above. Hence it can be seen thatmultipath reception can be controlled by choice of the physicaldimensions of the partitioning device, and the materials of the sectorvolume, the absorbers and the partition wall.

FIGS. 8-10 illustrate the analysis of the geometric configuration of theantenna elements 22 and partitioning device 20 in accordance with apreferred embodiment of the invention. FIG. 8 shows the geometry for theantenna array 21 based on a spherical design. Other geometries may beused since this example is for illustration purposes to show some of thebasic analysis and equations for the design of the antenna array 21. Thedesign in FIG. 8 starts out with a sphere 70. Chord AB 72 defines thebase plate of an antenna array. The distance n 74 is defined as thedistance from the arc of the circle to the chord AB 72. The length ofchord AB 72 is b. Together n and b define the dimensions of the antennaarray and the radius of the sphere 70. In particular, the radius, r 76,is defined from b and n by the following equation.

$\begin{matrix}{r = \frac{b^{2} + {4n^{2}}}{8n}} & (1)\end{matrix}$

The configuration for the individual antenna units, i.e., partitions, isthen developed by first considering the sky coverage desired. For thisexample, the coverage involves each antenna unit covering about half thecoverage of the adjacent antenna unit as seen from the side. This typeof configuration gives two possible types of which only the rectangularcoverage for minimum two antenna coverage is shown in FIG. 9. Thenumbers in FIG. 9 represent the numbers of antennas covering that area,hence the smallest number for an area is two. A planar arrangement isshown here for simplicity of illustration. The coverage can be optimizedfor different scenarios using irregular antenna unit placement, usingdifferent shapes, antenna units (L1, L2 or L5 GPS signals) and sizes,etc., instead of a one-size circular antenna reception pattern. Thediameters of the circles in FIG. 9 represent the field-of-view asrepresented by an angle of a cone with the vertex located at virtuallythe center of the antenna unit.

A representation of two of many antenna units is shown in FIG. 10. Theantenna elements are represented as point sources on the antenna arraysurface. This assumption is not a problem considering the largedistances from the antenna array to the orbit of a GPS satellite, forexample. The center axis for each antenna unit is shown. The purpose ofFIG. 10 is to show the relationships necessary to determine thefield-of-view (FOV) for each antenna unit and the necessary spacingbetween antenna units for a given Δδ_(i), which is the difference anglethat is formed by the chord with the center of the spherical design. Itis a parameter that is assigned to be common throughout all equationsand is formed from two angles δ_(i), and δ_(i-1). The equation for thedifference angle is:Δδ_(i)=δ_(i-1)−δ_(i)  (2)

The distance, r_(i) from the antenna array center to the surface, shownin FIG. 10 for each antenna unit is given as:r _(i)=√{square root over (r²+(r−n _(i))²−2r(r−n _(i)) cosδ_(i))}{square root over (r²+(r−n _(i))²−2r(r−n _(i)) cos δ_(i))}  (3)

The constraint equations for maintaining the proper sky coverage arebased upon the distance from an adjacent antenna to where the centeraxis of the antenna unit in question crosses the satellite orbit. Theseequations are given below as:

$\begin{matrix}\begin{matrix}{m_{i} = \sqrt{\begin{matrix}{{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} + q^{2} + {2{rq}\sqrt{1 - {\cos\;\Delta\;\delta_{i}}}}} \\\left\lbrack \frac{r_{i}^{2} - r_{i - 1}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{{- 2}r_{i - 1}r\sqrt{2\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} \right\rbrack\end{matrix}}} & (4) \\{\;{n_{i} = \sqrt{\begin{matrix}{{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} + q^{2} + {2{rq}\sqrt{1 - {\cos\;\Delta\;\delta_{i}}}}} \\{\left\lbrack \frac{r_{i - 1}^{2} - r_{i}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{{- 2}r_{i}r\sqrt{2\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} \right\rbrack\mspace{11mu}}\end{matrix}}}} & (5)\end{matrix} & \; \\\; & \;\end{matrix}$

To find the field-of-view, the formula of a general triangle is used torelate the three sides of the triangle to one angle. Since two sides forthe triangle containing the unknown angle AFOV_(i) are known, only thethird side is needed and can be found from the equations below fory_(i). The solution to y_(i) will be iterative due to the transcendentalnature of these equations.

$\begin{matrix}{y_{i} = \begin{bmatrix}{{\left\lbrack \sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} \right\rbrack\left\lbrack \frac{{- 2}n_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{q^{2} - n_{i}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}} \right\rbrack} -} \\\begin{bmatrix}{\left\lbrack \sqrt{\begin{matrix}{y_{i}^{2} + {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} - {2y_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}} \\\frac{q^{2} - n_{i}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{{- 2}n_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}\end{matrix}} \right\rbrack*} \\\begin{matrix}\left\lbrack \frac{q^{2} - m_{i}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{{- 2}m_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}} \right\rbrack \\\left\lbrack \frac{{- 2}n_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{q^{2} - n_{i}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}} \right\rbrack\end{matrix}\end{bmatrix}\end{bmatrix}} & (6)\end{matrix}$

An approximate solution for y_(i) for q≈m_(i)≈n_(i)>>r² is:

$\begin{matrix}{y_{i} \approx {{2n_{i}} - \sqrt{y_{i}^{2} + {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}\left( {1 - \frac{y_{i}}{n_{i}}} \right)}}}} & (7)\end{matrix}$

The equation for AFOV_(i) is:

$\begin{matrix}{{AFOV}_{i} = {\cos^{- 1}\left\lbrack \frac{\left. {\left( {n_{i} - x_{i}} \right)^{2} - q^{2} - y_{i}^{2}} \right)}{{- 2}{qy}_{i}} \right\rbrack}} & (8)\end{matrix}$

The field-of-view BFOV_(i) is found similarly as AFOV_(i). First thethird side is found as

$\begin{matrix}{x_{i} = {\sqrt{\begin{matrix}{y_{i}^{2} + {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} - {2y_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}} \\\frac{q^{2} - n_{i}^{2} - {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}{{- 2}n_{i}\sqrt{2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}}\end{matrix}}\;}} & (9)\end{matrix}$

An approximate solution for x_(i) for q≈n_(i)>>r² is

$\begin{matrix}{x_{i} \approx \sqrt{y_{i}^{2} + {2{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}} - \frac{2y_{i}{r^{2}\left( {1 - {\cos\;\Delta\;\delta_{i}}} \right)}}{n_{i}}}} & (10)\end{matrix}$

The equation for BFOV_(i) is

$\begin{matrix}{{BFOV}_{i} = {\cos^{- 1}\left\lbrack \frac{\left( {m_{i} - y_{i}} \right)^{2} - q^{2} - x_{i}^{2}}{{- 2}{qx}_{i}} \right\rbrack}} & (11)\end{matrix}$

The passive anti-jamming antenna system of the present invention may beimplemented using little or no software. The multiple antenna elementsmay be controlled by simple software logic, which controls theattenuation of the signal if the power exceeds a threshold. Powersensitive RF filters or power reactive RF lenses or composites may alsobe used to evaluate and attenuate the signal in each sector. Forexample, two or more layers of orthogonally polarized materials may beemployed that permit target frequencies below an application-specificpower threshold to pass through, but attenuate target frequencies upondetection that the threshold is exceeded. The layers may also havehysteresis properties with respect to signal attenuation and transfersufficient to meet protected system requirements.

Furthermore, an outer protective skin may be provided that is composedof a material that protects the antenna system or provides aerodynamicqualities. This skin may also serve as a band-pass filter, limiting thefrequencies passing through to the subtending cell to a band-width thatincludes the targeted frequency. Alternatively, an inner structure of RFdirective lenses may be employed which have the followingcharacteristics: they partition the RF environment; are coated orotherwise designed to prevent RF reflections and multipath receptions;permit target frequencies below application-specific power threshold topass through; and attenuate target frequencies upon detection that thethreshold is exceeded through reflection (directing excess power awayfrom the protected antenna receiver element).

Numerous other modifications to and alternative embodiments of thepresent invention will be apparent to those skilled in the art in viewof the foregoing description. Accordingly, this description is to beconstrued as illustrative only and is for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Detailsof the structure and method may be varied substantially withoutdeparting from the spirit of the invention and the exclusive use of allthe modifications, which come within the scope of the appended claims,is reserved.

1. In an environment comprising a plurality of sources ofelectromagnetic energy, an antenna system comprising: a plurality ofreceiving antenna elements; a partitioning structure: positioned betweenthe elements and the sources, disposed to create at least twonon-identical radio frequency fields of view; and at least one absorbersubstantially lining at least wall of the partitioning structure.
 2. Theantenna system according to claim 1, further comprising: a processingunit: in electrical communication with at least two antenna elements;operative to receive the electrical signal of each communicated antennaelement; operative to characterize the electrical signal of eachcommunicated antenna element; and operative to modify those electricalsignals for which the characterization meets a condition.
 3. The antennasystem according to claim 2, wherein the characterization of theelectrical signal of each communicated antenna element comprises afunction of the power such electrical signal.
 4. The antenna systemaccording to claim 3, wherein the condition for modification is that thefunction of the power of the characterized electrical signal exceeds athreshold.
 5. The antenna system according to claim 4, wherein themodification of those electrical signals for which power is greater thana threshold is attenuation.
 6. The antenna system according to claim 5,wherein the modification of those electrical signals for which power isgreater than a threshold is blocking.
 7. The antenna system according toclaim 2, further comprising, a combiner: in electrical communicationwith at the processing unit; and operative to receive at least twoelectrical signals from the processing unit and combine the signals. 8.The antenna system according to claim 1, further comprising an outerskin substantially covering at least a portion of the partitioningstructure.
 9. The antenna system according to claim 8, wherein the outerskin is a bandpass filter.
 10. The antenna system according to claim 1,wherein the partitioning structure comprises a plurality of hex-shapedwalls.
 11. In an antenna system comprising a plurality of antennaelements, a method for improving the resistance of the antenna system tointerference from electromagnetic energy sources, the method comprising:physically partitioning, using a partitioning structure, the spacebetween the receiving antenna array and the electromagnetic energysources such that at least two antenna elements are characterized bynonidentical radio frequency fields of view; and substantially coatingat least one surface of the partitioning structure with an absorber. 12.The method according to claim 11, further comprising: in response toelectromagnetic energy incident on the antenna array, determining whicharray elements contain energy characteristic of interference; andmodifying the signal from at least one array element that containsenergy characteristic of interference.
 13. The method according to claim12, wherein the step of modification comprises broadband attenuation ofthe signal from at least one antenna element that contains energycharacteristic of interference.
 14. The method according to claim 12,wherein the step of modification comprises blocking the electromagneticenergy from at least one antenna element that contains energycharacteristic of interference.